1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that includes a sensor for detecting contact with a recording medium.
2. Description of Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure where a read head unit having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head unit includes a main pole that produces a magnetic field in a direction perpendicular to the plane of the recording medium. The main pole includes, for example, a track width defining portion having an end located in a medium facing surface that faces the recording medium, and a wide portion that is connected to the other end of the track width defining portion and is greater in width than the track width defining portion. The track width defining portion has a generally constant width. To achieve higher recording density, it is required that the write head unit of the perpendicular magnetic recording system be smaller in track width and improved in write characteristics such as an overwrite property which is a parameter indicating an overwriting capability.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). The slider is designed to slightly fly over the surface of the recording medium by means of an airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air outflow end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks that are adjacent to a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing (such a phenomenon will hereinafter be referred to as adjacent track erase). To increase the recording density, it is required to prevent the occurrence of adjacent track erase.
Providing a write shield near the main pole is effective for preventing the aforementioned skew-induced adjacent track erase and increasing the recording density. For example, U.S. Pat. No. 6,954,340 B2 and U.S. Patent Application Publication No. 2005/0128637 A1 describe a magnetic head including a write shield having an end face that is located in the medium facing surface to wrap around an end face of the main pole.
A magnetic head including a write shield is typically provided with one or more return path sections for connecting the write shield to a part of the main pole away from the medium facing surface. The one or more return path sections include a yoke layer extending in a direction perpendicular to the medium facing surface. The write shield and the one or more return path sections function to capture a magnetic flux that is produced from the end face of the main pole and that expands in directions other than the direction perpendicular to the plane of the recording medium, and to thereby prevent the magnetic flux from reaching the recording medium. The write shield and the one or more return path sections also function to allow a magnetic flux that has been produced from the end face of the main pole and has magnetized the recording medium to flow back to the main pole. Thus, the magnetic head including the write shield allows prevention of the adjacent track erase and allows a further improvement in recording density.
U.S. Pat. No. 6,954,340 B2 and U.S. Patent Application Publication No. 2005/0128637 A1 describe a magnetic head including, as the aforementioned one or more return path sections, a return path section located forward along the direction of travel of the recording medium (i.e., on the trailing end side) relative to the main pole, and a return path section located backward along the direction of travel of the recording medium (i.e., on the leading end side) relative to the main pole.
For a magnetic disk drive, it is desired that the distance from the read head unit and the write head unit to the surface of the recording medium be small and constant in order to suppress a decrease in reading capability and writing capability. To meet this, there has been proposed a slider that includes a heater to be energized for heat generation, as disclosed in, for example, JP-A-2008-77751. In the slider including the heater, part of the magnetic head expands with the heat generated by the heater, so that the medium facing surface protrudes in part. This makes it possible to reduce the distance from the read head unit and the write head unit to the surface of the recording medium, and to control the distance from the read head unit and the write head unit to the surface of the recording medium by heater control.
When part of the medium facing surface is protruded as described above, it becomes easier for the part of the medium facing surface to make contact with the surface of the recording medium. The recording medium sometimes has minute projections on its surface. In such a case, part of the medium facing surface may make contact with the projections on the surface of the recording medium, though not with the areas other than the projections. If the recording medium is wavy in the surface, part of the medium facing surface can make contact with certain areas on the surface of the recording medium. Since the contact of part of the medium facing surface with the surface of the recording medium hinders normal read and write operations, it is necessary to avoid such a contact.
Thus, prior to shipment of the magnetic disk drive product, a test may be performed to detect the areas of the surface of the recording medium with which part of the medium facing surfaces makes contact, with the amount of protrusion of the part of the medium facing surface maintained constant. This makes it possible to manufacture a product that is programmed to reduce the amount of protrusion of the part of the medium facing surface when the magnetic head passes the areas of contact detected by the test, so as to avoid contact.
The foregoing test needs a sensor for detecting a contact between part of the medium facing surface and the surface of the recording medium. JP-A-2008-77751 describes a slider including a heat generating resistance part that functions as both a heater and a sensor, and a thermal conduction layer disposed above or under the heat generating resistance part.
Here, consider a case where a heater and a sensor are provided in a magnetic head that is configured so that the write head unit is located forward of the read head unit along the direction of travel of the recording medium and the write head unit includes a return path section located backward of the main pole along the direction of travel of the recording medium. In this case, it is appropriate to dispose the sensor between the read head unit and the write head unit. If so configured, however, the following problem arises due to the presence of the yoke layer of the return path section.
First, the sensor needs to be disposed in the vicinity of the area of the medium facing surface where the amount of protrusion is large. It is therefore preferred that in the vicinity of sensor there exist a layer that makes a large amount of expansion toward the recording medium when subjected to the heat generated by the heater. Suppose that the sensor is provided between the read head unit and the write head unit in a magnetic head that has the aforementioned return path section. In such a case, since the yoke layer of the return path section lies between the read head unit and the main pole, it would be advantageous if the yoke layer could make a large expansion toward the recording medium with the heat generated by the heater. The yoke layer, however, is connected to the write shield and the main pole. This suppresses expansion of the yoke layer toward the recording medium. As thus described, if the sensor is provided between the read head unit and the write head unit in the magnetic head having a yoke layer between the read head unit and the main pole, the yoke layer prevents the medium facing surface from protruding in part. This gives rise to the problem that it becomes difficult to control the distance from the read head unit and the write head unit to the surface of the recording medium and detect the contact of part of the medium facing surface with the recording medium effectively.